The aim of these investigative studies is the continuation of research on various aspects of viral carcinogenesis with special reference to simian virus 40 (SV40). This undertaking has been pursued by the Principal Investigator for the past 12 years (1963-1975). IN the immediate future the following phenomena will be investigated: (1) The relative role of the target (hamster) cell versus that of the viral (SV40) genome in determining morphogenesis and the differentiated state of SV40-induced neoplasms. (2) The importance of the presence of the viral (SV40) genome in the development and severity of oncogenicity in the SV40-hamster cell system. (3) The interrelation of the various SV40-mediated cellular "neoantigens", and their significance in the persistence of the oncogenic state. BIBLIOGRAPHIC REFERENCES: Diamandopoulos, G.Th. and McLane, M.-F.: Effect of Host age, virus dose, and route of inoculation on tumor incidence, latency and morphology in Syrian hamsters inoculated intravenously with oncogenic DNA simian virus 40. J. Nat. Cancer Inst. 55:479-482, 1975. Diamandopoulos, G.Th., Miller, M.H., McLane, M.-F., and Evans, P.G.: Loss or persistence of the differentiated state of SV40-induced hamster tumor cells before and after serial passage in culture. Cancer Research (submitted, Nov. 1975).